Nodes without private IPs

Allow nodes to have no private IPs.
Nodes without private IPs will automatically be put into
their own location.

pkg/k8s/backend.go

@@ -209,7 +209,11 @@ func (nb *nodeBackend) Set(name string, node *mesh.Node) error {
 	}
 	n := old.DeepCopy()
 	n.ObjectMeta.Annotations[endpointAnnotationKey] = node.Endpoint.String()
-	n.ObjectMeta.Annotations[internalIPAnnotationKey] = node.InternalIP.String()
+	if node.InternalIP == nil {
+		n.ObjectMeta.Annotations[internalIPAnnotationKey] = ""
+	} else {
+		n.ObjectMeta.Annotations[internalIPAnnotationKey] = node.InternalIP.String()
+	}
 	n.ObjectMeta.Annotations[keyAnnotationKey] = string(node.Key)
 	n.ObjectMeta.Annotations[lastSeenAnnotationKey] = strconv.FormatInt(node.LastSeen, 10)
 	if node.WireGuardIP == nil {
@@ -289,6 +293,8 @@ func translateNode(node *v1.Node, topologyLabel string) *mesh.Node {
 		// remote node's agent has not yet set its IP address;
 		// in this case the IP will be nil and
 		// the mesh can wait for the node to be updated.
+		// It is valid for the InternalIP to be nil,
+		// if the given node only has public IP addresses.
 		Endpoint:            endpoint,
 		InternalIP:          internalIP,
 		Key:                 []byte(node.ObjectMeta.Annotations[keyAnnotationKey]),

pkg/k8s/backend_test.go

@@ -187,6 +187,33 @@ func TestTranslateNode(t *testing.T) {
 			},
 			subnet: "10.2.1.0/24",
 		},
+		{
+			name: "no InternalIP",
+			annotations: map[string]string{
+				endpointAnnotationKey:    "10.0.0.1:51820",
+				internalIPAnnotationKey:  "",
+				keyAnnotationKey:         "foo",
+				lastSeenAnnotationKey:    "1000000000",
+				locationAnnotationKey:    "b",
+				persistentKeepaliveKey:   "25",
+				wireGuardIPAnnotationKey: "10.4.0.1/16",
+			},
+			labels: map[string]string{
+				RegionLabelKey: "a",
+			},
+			out: &mesh.Node{
+				Endpoint:            &wireguard.Endpoint{DNSOrIP: wireguard.DNSOrIP{IP: net.ParseIP("10.0.0.1")}, Port: 51820},
+				InternalIP:          nil,
+				Key:                 []byte("foo"),
+				LastSeen:            1000000000,
+				Leader:              false,
+				Location:            "b",
+				PersistentKeepalive: 25,
+				Subnet:              &net.IPNet{IP: net.ParseIP("10.2.1.0"), Mask: net.CIDRMask(24, 32)},
+				WireGuardIP:         &net.IPNet{IP: net.ParseIP("10.4.0.1"), Mask: net.CIDRMask(16, 32)},
+			},
+			subnet: "10.2.1.0/24",
+		},
 	} {
 		n := &v1.Node{}
 		n.ObjectMeta.Annotations = tc.annotations